In molecular diagnosis, the target DNA or RNA sequences in a sample are frequently at very low concentrations, which can be around or below the detection limit of available clinical diagnostic methods. This renders the analysis of these samples unreliable, or impossible. Currently, the detection limit of available methods is at the level about 105 copies of the target sequence in a sample. However, a concentration of certain DNA and RNA sequences in a sample substantially below this level can be clinically significant.
The well-known PCR method was developed for solving this specific problem. In general, PCR based assays increase the concentration of a target sequence from its original concentration in the sample, and subsequently measure the target sequence after the amplification. However, PCR based assays have complicated and lengthy sample preparation process, and require highly trained laboratory personals. The PCR based assays typically require up to 24 hours to obtain the analysis results.
It is desirable to be able to enhance the detectable signals of low concentration nucleic acids and to reduce the current detection limits without amplifying the concentration of the target sequence.